OFDM ambiguity function improvement with FBMC prototype filter for passive radar

Orthogonal Frequency Division Multiplexing (OFDM) based waveform has been widely used as illuminator of opportunity in passive radar systems. Ambiguity function (AF) of OFDM is shown to be nearly perfect thumbtack shaped except for the undesirable high side lobes in the Doppler dimension. In this paper, we propose a novel filtered OFDM scheme to improve OFDM AF by utilizing Filtered Bank Multi-Carrier (FBMC) prototype filter. We derive the cross ambiguity function (CAF) between OFDM and filtered OFDM. And then we conclude that the weighting network whose power spectrum density decays faster achieves better CAF performance. Simulation results are presented to validate the conclusion. Specifically, FBMC prototype filter is superior to the classical Bartlett and Hanning weighting networks in terms of suppressing OFDM AF's high Doppler side lobes with nearly no cost of Doppler bandwidth.